In most localities, commercial establishments such as taverns and restaurants are no longer permitted to wash beverage glasses by hand, and the machines by which such glasses are washed are required to meet standards set by the National Sanitation Foundation. These standards require that glasses be subjected to a thorough soil-removing spray of a detergent solution at a temperature of at least 120.degree. F., followed by a thorough spray with a germicidal rinsing solution.
It is obvious that total sanitization of beverage glasses cannot be consistently and assuredly achieved with a glass washing machine that has one or more of its spray nozzles blocked by foreign matter that prevents or substantially reduces the discharge of cleansing liquid. In relation to the very important public health implications of such spray nozzle blockages, the prior art relating to glass washing machines reflects a disproportionately small attention to the problem. Glasses to be washed in a tavern or restaurant often contain foreign matter such as berry seeds, fruit pulp or bits of paper napkin that is washed off of them and carried in the cleansing liquid discharged from certain of the nozzles. In machines wherein such cleansing liquid is collected in a retention tank and pumped back to those nozzles, a screen is usually provided through which the collected liquid must pass before it arrives at the recirculation pump, intended to prevent foreign matter from being carried back to the nozzles and blocking them. Most such screens heretofore provided have had some deficiency. In some cases, the screen permitted some foreign matter to escape and pass into the nozzles; in other cases the screen was so arranged that foreign matter trapped by it could fall into the recirculation outlet when the screen was removed for cleaning; and in many cases the screen could be readily blocked by foreign matter to such an extent that there was a substantially diminished flow back to the nozzles through it, so that there was insufficient discharge from the nozzles even though they themselves were not blocked. As a result of these deficiencies, it is known that glass washing machines have often been permitted to operate--sometimes for prolonged periods--with an unnoticed or disregarded blockage that resulted in incompletely cleansed glasses.
The above mentioned copending application, Ser. No. 117,155, discloses effective screening means for assuredly preventing blockage of nozzles by foreign matter carried in recirculated cleansing liquid and for causing the machine to shut down in response to any condition that might cause a diminished flow of recirculated liquid back to nozzles from which such liquid had been discharged.
But even with absolute assurance against blockage by solid or semi-solid materials, the nozzles of a glass washing machine can in time become partially or wholly blocked by substances normally dissolved in the cleansing liquid itself. In an efficient glass washing machine such as is disclosed in each of the above mentioned Ser. Nos. 117,155 and 136,133, hot detergent solution is discharged from a set of washing nozzles while cooler germicidal solution is discharged from a set of rinsing nozzles, and such discharge continues for a predetermined interval, on the order of 30 seconds to 2 minutes. The machine then shuts down and remains out of operation for an indefinite period that may range from a few seconds to several hours. When the machine stops, liquid drains away from all of the nozzles, leaving them wet. During the subsequent period of shutdown, the water component tends to evaporate out of the solutions that wet the nozzles, leaving on them residue deposits that may partially block their outlets. When the machine is restarted, the hot detergent solution that flows through the washing nozzles tends to dissolve the residue on them rather quickly, and therefore blockage of the washing nozzles by residue deposits is seldom a problem, although it can occur. However, the germicidal chemical in the rinsing solution seems to react with minerals naturally present in many water supplies, and especially with the iron often present in well water, producing a precipitate residue that is not readily dissolved by the rinsing solution itself. Hence, the residue on the rinsing nozzles, instead of being washed away during each operating cycle, tends to build up through successive cycles until the discharge of rinsing solution is eventually reduced to such an extent that glasses put through the machine are not properly sanitized. Since the outlet opening in a glass washer spray nozzle is very small--typically about 1 mm diameter--only a relatively small buildup of residue can materially reduce the rate of discharge from such a nozzle.
Thus, satisfactory operation of a glass washing machine requires periodic cleaning of all of its spray nozzles. Prior glass washing machines have made no provision for such cleaning of the nozzles, other than to arrange the nozzle assemblies for more or less ready removal to facilitate manual cleaning. This was a serious deficiency because discharges from the nozzles ordinarily cannot be observed while the machine is in operation, and therefore the need for nozzle cleaning did not become apparent until the performance of the machine had deteriorated to the point of being hazardous to public health. Even then, the difficult and tedious work needed to correct the condition tended to discourage prompt action.